Air filters positioned within or as part of an air intake system for an engine provide filtered air for the engine. The air filters may clog due to accumulation of dust or frost. Clogged air filter may lead to decreased manifold air pressure, and deteriorate fuel economy and drivability. Monitoring air filter condition may provide an early indication of the remaining useful life of the air filter and help car owner plan maintenance ahead of time.
Other attempts to address air filter clogging include determining filter clogging based on pressure difference across the air filter. One example approach is shown by Freen et al. in U.S. 20110185895A1. Therein, a differential pressure sensor measures a pressure differential between a first pressure upstream of the air filter and a second pressure downstream of the air filter. Filter condition is then determined by comparing the pressure differential with a baseline pressure differential.
However, the inventors herein have recognized potential issues with such systems. As one example, Freen requires a battery powered probe to measure the pressure differential across the air filter. In naturally aspired engines, differential pressure sensor is generally not present around the air filter. The additional probe in Freen may add complexity and cost to the engine system. Further, Freen requires re-calibration of the baseline pressure differential by a user whenever a new filter is installed. If the re-calibration is not timely performed, Freen's method may lead to incorrect estimation of filter condition.
In one example, the issues described above may be addressed by a method comprising: routing air through an air filter into a manifold; during steady state condition, estimating an air filter resistance based on an air charge value in the manifold, the air filter resistance being inversely proportional to the square of a mass air flow through the air filter; and indicating air filter condition based on the air filter resistance. In this way, air filter clogging may be determined during steady state condition without requiring additional sensor.
As one example, an observer may be constructed for estimating an air filter resistance of an air filter coupled to the intake passage of an engine system. Air filter condition may be determined based on the air filter resistance. For example, filter clogging may be determined in response to air filter resistance higher than a threshold. The air filter resistance may be inversely proportional to the square of a mass air flow through the air filter and proportional to a pressure difference across the air filter. As such, the air filter resistance may characterize filter clogging regardless filter geometry or material properties. In other words, air filter condition may be determined by the air filter resistance even when different types of filters may be used. The air filter resistance may be estimated based on an air charge value in the manifold via the observer. In non-boosted applications, either a mass air flow (MAF) sensor downstream of the air filter or a manifold air pressure (MAP) sensor downstream of a throttle may present in the engine system for monitoring the air charge. During steady state condition, the mass air flow through the intake manifold may be the same as the mass air flow through the air filter and the mass air flow through the throttle. Thus, based on availability of the sensor, during steady state condition, the manifold air charge value may be a MAF measured by the MAF sensor or a MAP measured by the MAP sensor. If the manifold air charge value is the MAF, the observer may estimate system states including the resistance of the air filter, a pressure immediately downstream of the air filter, and the MAP simultaneously. If the manifold air charge value is the MAP, the observer may estimate system states including the resistance of the air filter and the pressure immediately downstream of the air filter simultaneously. In this way, air filter condition may be determined based on the manifold air charge value measured by the sensor already existed in the engine system. The observer may estimate the resistance of the air filter without the knowledge of throttle position. Further, air filter condition may be determined online without interrupting engine operation.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.